This invention relates to the design and circuit implementation of adaptive equalizers, which are used in modern electrical communication to equalize (i.e., compensate for) linear amplitude and phase distortions which occur naturally within the useful frequency band of practical transmission circuits. If these distortions are compensated, as is well known in the art, a given circuit is capable of correctly received transmission of information at substantially higher rates and over virtually unlimited transmission distances.
In particular, the invention relates to dynamically adaptive equalizers, which employ the signals transmitted through a communication circuit or channel for measurement of its distortion. Such circuits alter their amplitude and phase characteristics with time to minimize the measured error at the receiving end of the circuit. Adaptive equalizers are required for use in connection with circuits whose distortion properties are unknown at the time of initiation of transmission, or which for any reason may change during transmission. Representative circuits include those having variable multiple paths, radio transmissions carrying digital voice, data and other signals, and switched telephone lines. In typical adaptive equalizer operation, communication may be established using a repeated signal carrying no information. The equalizer adjusts rapidly to compensate for the transmission circuit distortion. After information transmission is begun, the information signals are then used continuously for iterative dynamic correction of the filter characteristics.
More specifically, this invention relates to adaptive equalizers implemented using digital sampling and computation processes to effect equalization of transmission lines, or to remove signal distortion due to variable and multiple paths, in radio transmissions carrying digital voice, data and other signals.